1. Field of the Invention
The present invention relates to protocols and systems for establishing a packet switched network model connection between a mobile terminal device and a packet network via a wireless connection formed between a wireless communication device and a base station.
2. Description of Background Information
Mobile computing generally involves the use of mobile terminal devices such as notebook computers connected to computing resources via a wireless communication device. As mobile computing becomes more prevalent, traveling users will be provided continuous connectivity, and thus full access, to their computing resourcesxe2x80x94data and files stored at their office LAN, email servers, etc. To make this a reality, efforts abound to develop and introduce new data services and technologies.
FIG. 1 is a block diagram of a simplified network reference model applicable to mobile computing data services. The model shows select network entities forming a communications subsystem 10. A mobile terminal device 12 is coupled to a wireless communication device 14, which is in turn connected to a base station/mobile switching center 16 via a wireless interface. Base station/mobile switching center 16 is connected to an interworking function 18. The simplified network reference model is described in the document entitled xe2x80x9cData Service Options for Wideband Spread Spectrum Systems,xe2x80x9d TIA/EIA/IS-707, Published Version (February 1998), (hereinafter referred to as xe2x80x9cIS-707xe2x80x9d) as well as in the newer version thereof, i.e., IS-707-A. The content of each of IS-707 and IS-707-A is hereby expressly incorporated by reference herein in its entirety.
According to IS-707, mobile terminal device 12, wireless communication device 14, base station/mobile switching center 16, and interworking function 18 are respectively referred to as a TE2 device, an MT2 device, a BS/MSC, and an IWF. The interface between mobile terminal device 12 and wireless communication device 14 is called an Rm interface. The interface between wireless communication device 14 and base station/mobile switching center 16 is referred to as a Um interface. The interface between base station/mobile switching center 16 and interworking function 18 may be implemented with an L interface.
Mobile terminal device 12 may comprise, for example, a notebook computer, a personal digital assistant, or any other computing device capable of computer network communications, including packet-based communications or communications via a dial-up modem. Wireless communication device 14 may comprise, for example, a wireless terminal used by subscribers to access network services over a radio link. The wireless terminal may comprise a hand-held cellular telephone, or a unit installed in a vehicle. Wireless communication device 14 may also be fixed to a particular location.
Base station/mobile switching center 16 is shown in FIG. 1 as a single functional entity, although it need not be. The base station portion of the illustrated base station/mobile switching center allows wireless communication device 14 to access network services using a radio link or another type of wireless link. The mobile switching center portion handles the switching of traffic between the wireless link and a telecommunications network to which the wireless link is connected. The telecommunications network may comprise one or a combination of PSTN, ISDN, internet routers, and other network types and network entities.
Interworking function 18 represents the point at which a gateway or bridge connection is formed between mobile terminal device 12 and/or wireless communication device 14 at one end and an internetwork at the other end.
FIG. 2 is a simplified diagram of a protocol stack adhered to by many mobile computing environments, including those adhering to IS-707, RFC 1332, xe2x80x9cThe PPP Internet Protocol Control Protocol (IPCP)xe2x80x9d (May, 1992), RFC 1661, xe2x80x9cThe Point-To-Point Protocol (PPP)xe2x80x9d (July, 1994), and RFC 2002, xe2x80x9cIP Mobility Supportxe2x80x9d (October, 1996). The stack comprises one or more lower layer(s) 28, a data link layer 26, a network layer 24, and one or more upper layers 22. One or more lower layers 28 are provided, including, at the lowest layer, connections establishing a physical link. The relay layer disclosed in IS-707 is included in these lower layers above the physical layer.
Data link layer 26 is immediately above lower layer(s) 28. Data link layer 26 may utilize such protocols as PPP and/or SLIP. This layer deals with point-to-point communications between computers. It packages addressing data and manages the flow of transmissions. PPP (the point-to-point protocol) is described, for example, in RFC 1332 (May, 1992), the content of which is hereby expressly incorporated by reference herein in its entirety. PPP facilitates the transmission of datagrams between data communications equipment from different manufacturers over dial-up and dedicated serial point-to-point links. PPP can simultaneously transmit multiple protocols across a single serial link, without the need to set up a separate link for each protocol. PPP also allows the interconnection of dissimilar devices, such as host bridges and routers, over serial links. The PPP protocol is comprised of three main components, including an encapsulation scheme, a link control protocol, and network control protocols. These components are respectively responsible for creating the frame, controlling the link, and managing the network layer protocol.
Network layer 24 is just above data link layer 26, and may comprise such protocols as IP or CLNP. The network layer ensures that information arrives at its intended destination. That is, it is concerned with the actual movement of information from one network entity to another. The network layer is responsible for getting data from one computer to another. The internet protocol (IP) breaks up data messages into packets, routes the packets from a sender to a destination network entity, and reassembles the packets into the original data messages at the destination. The IP protocol contains an IP header which contains source and destination address fields that uniquely identify host computers respectively acting as the source and destination of the packets being transferred.
Upper layer(s) portion 22 comprises one or more protocol layers above network layer 24, including, for example, the TCP (transmission control protocol) protocol which is responsible for reliable, in-order delivery of data from one application to another.
Two types of mobile data calls may be placed by a mobile terminal device 12 through a wireless communication device 14: circuit switched (including fax calls) and packet switched. In a circuit switched mobile data call, a circuit switched connection is made between mobile terminal device 12 and a given target network. Mobile terminal device 12 makes this connection by establishing a dial-up modem connection directly over a circuit switched network to a modem-accessible target networkxe2x80x94e.g., to an internet service provider (ISP) or to an office network or LAN. In a packet switched call, a direct connection is established between mobile terminal device 12 at one end and a packet network at the other end through interworking function 18.
There are generally two modes of operation in which packet switched calls can be placed: the network model and the relay model. In a relay model packet call, a packet switched connection is made between mobile terminal device 12 and the network through interworking function 18, while wireless communication device 14 acts as a conduit, at the physical layer. Accordingly, if there is a change in the connection between interworking function 18 and wireless communication device 14 (e.g., the physical link therebetween is temporarily interrupted), the call may be dropped between mobile terminal device 12 and interworking function 18.
On the other hand, in a network model packet call, two separate PPP links are provided at the data link layer: a first interface data link is formed within the data link layer across the Rm interface, and a second interface data link is formed within the data link layer across the Um interface (as well as across the L interface). The separate PPP links help support xe2x80x9ctransparent mobility;xe2x80x9d that is, the mobile terminal device 12 does not need to know when its location changes so as to affect the link between wireless communication device 14 and interworking function 18. In other words, the network model mode of operation prevents changes over the Um link from affecting the Rm link, as the Rm link is isolated from the Um link. This helps with the support of transparent mobility. Another benefit is that the TE2 is protected from arbitrary PPP renegotiations.
The establishment of separate and isolated PPP links at the data link layer over the Rm and the Um interfaces is only part of what is necessary to support transparent mobility. A network layer connection must also be established between mobile terminal device 12 and interworking function 18 at the network layer in a way that still supports transparent mobility.
3. Definitions of Acronyms and Terms
The following term and acronym definitions are provided to assist the reader in obtaining an understanding of the invention as described herein.
Flow Control: Performed by the receiving entity to limit the amount or rate of data sent to it by a transmitting entity or to ignore messages it receives while keeping the transmitting entity unaware that it is being ignored.
Interworking Function (IWF): A point at which a gateway or bridge connection is form ed between a given network (e.g., a packet network) and mobile devices coupled to the network by way of a base station and/or a mobile switching center.
In view of the above, the present invention, through one or more of its various aspects and/or embodiments, is thus presented to bring about one or more objects and advantages. One such object is to provide mechanisms and protocols which facilitate the establishment of a packet link between a mobile terminal device and a network via an interworking function, while supporting transparent mobility so that changes over the Um link do not affect the Rm link. A further object of the present invention is to provide such mechanisms and protocols which also allow for IP mobility support.
The present invention, therefore, is directed to a system or a method for establishing a packet network call over a transmission link extending between a mobile terminal device and an interworking function. The transmission link connects the mobile terminal device to a wireless communication device over a first interface, and further connects the wireless communication device to the interworking function over a second interface via a wireless link to a base station. The packet network call, once established, comprises a first interface data link formed within a data link layer across the first interface and a second interface data link formed within the data link layer across the second interface. A flow control is asserted and deasserted on the mobile terminal device, and during the flow control, the wireless communication device performs a link control protocol negotiation with the interworking function to establish the second interface data link with the interworking function. After the second interface data link is established, and during the flow control, the wireless communication device performs a network control protocol negotiation with the interworking function entity to establish a second interface network link carried by the second interface data link, resulting in an IP address being assigned to identify the mobile terminal device. After the second interface data link is established, the mobile terminal device performs a link control protocol negotiation with the wireless communication device to establish the first interface data link with the wireless communication device. After the first interface data link and the second interface network link are each established, the mobile terminal device performs a network control protocol negotiation with the wireless communication device to establish a first interface network link carried by the first interface data link, utilizing the same IP address assigned during the network control protocol negotiation with the interworking function.
Other acts are performed after the first interface and the second interface network link are each established, when the wireless communication device receives a request for a static IP address from the mobile terminal device. A determination is made as to whether mobile IP is supported by the packet network, and when mobile IP is not supported, the other acts are not performed. During a flow control on the mobile terminal device, the wireless communication device performs a network control protocol renegotiation with the interworking function to reestablish the second interface network link carried by the second interface data link using the static IP address. A network protocol negotiation is thereafter performed between the mobile terminal device and the wireless communication device to establish the first interface network link using the static IP address.